A. Technical Field
The present invention relates to authenticating electronic devices and, more particularly, to systems, devices, and methods of authenticating electronic devices by applying asymmetric cryptography schemes to Physically Unclonable Function (PUF)-based authentication ICs.
B. Background of the Invention
A traditional authentication IC is a device designed to securely hold a cryptographic key or secret in Non-Volatile Memory (NVM) or generate a secret via a PUF circuit that is integrated with the device. PUF design takes advantage of small but inevitable characteristic manufacturing variations in physical semiconductor components, including measurable variations in doping concentrations, gate oxide thickness, and tolerances in geometry that result from imperfect semiconductor manufacturing processes that electronic devices such as MOS devices undergo. These variations can be used to produce sequences of random, unique data values that can be used to generate cryptographic keys. A PUF circuit typically generates a random, device-unique but repeatable number that can be used to generate a unique response for verification purposes. The response unpredictably changes—hence the term unclonable—when the physical condition of the PUF circuit even slightly changes (e.g., due to minor physical damage) once the device containing the PUF circuit is probed or altered.
Two basic types of authentication ICs exist. A first type is based on symmetric cryptographic methods in which a unit authenticating a device, e.g., a host such as a printer, shares a secret with a device, e.g., a cartridge. The second type—the main subject of the present invention—is based on asymmetric cryptographic methods, wherein the entity authenticating a device uses a public key, and wherein the device uses a private key to prove its identity. While the public key may be freely disclosed, the private key must be strongly protected from disclosure.
Authentication ICs that store the secret in a NVM typically include some protection against reverse engineering. Nevertheless, common authentication ICs suffer from a significant shortfall, because given sufficient time, money, and expertise, adversaries can defeat existing protection mechanisms and retrieve even well-protected credentials such as private keys and clone devices, for example, by employing failure analysis techniques.
Since PUFs are known to provide the highest level of resistance against physical and invasive attack via reverse engineering, PUF-generated secrets are considered immune to these types of attacks. However, traditional authentication ICs that use PUF-generated secrets require the to-be-protected device carrying the IC be online such as to access the manufacturer's database to perform the authentication, which is neither always possible, nor convenient, nor secure.
Alternative approaches operate by generating a private key without using a PUF circuit or using a secret stored in non-volatile memory. However, such approaches are not immune to reverse engineering, at all, and can be bypassed by sophisticated attackers.
What is needed are systems and methods to overcome the abovementioned limitations.